This invention relates, in general, to CMOS circuits, and more particularly, to a CMOS polarity reversal circuit.
Often it is desirable to prevent reverse power from being applied to a circuit or an electronic instrument. In order to prevent such reversal of power into a circuit, the circuit's power terminals have been arranged in a manner to make it difficult for an individual to apply power to a circuit of polarity which would be harmful to the circuit. Also, the terminals have been color coded to indicate proper polarity of the input voltage. However, these precautions do not always eliminate circuit damage which is caused through inexperience or inadvertence.
More recently, using semiconductor bipolar components, bridges have been used, especially diode bridges, to prevent damage to a circuitry caused by polarity reversals of the input voltage. The use of bipolar components in a CMOS circuit entails additional manufacturing steps and consumes a relatively considerate amount of semiconductor area since the bipolar components have to be isolated from the CMOS components. Accordingly, it will be appreciated that it would be desirable to have a CMOS circuit capable of providing an output voltage of proper polarity regardless of the polarity of the input voltage.
Accordingly, it is an object of the present invention to provide a CMOS polarity reversal circuit which provides a proper polarity output voltage regardless of the polarity of the input voltage.
Another object of the present invention is to use P-channel and N-channel MOS devices to sense polarity of an input voltage and to provide output voltage in a predetermined polarity.
Yet another object of the present invention is to provide a CMOS polarity reversal circuit which has a minimum voltage drop across the reversal circuit itself.